Correlation between tyre/road noise levels measured by the Coast-By and the Close-ProXimity methods

The paper deals with the relationships between tyre/road noise levels measured by the Coast-By (CB) and the Close-ProXimity (CPX) methods. For that purpose, tyre/road noise was measured for a passenger car fitted with four identical patterned tyres rolling on a set of 15 impervious road surfaces. The CPX and CB measurement methods have been used simultaneously on each road surface at vehicle speeds ranging between 50 km/h and 110 km/h. A very good correlation between overall CPX and CB noise levels recomposed between 400 Hz and 4000 Hz was observed which is consistent with previous results of the literature. With the whole set of road surfaces and frequencies, a fairly good correlation between the CPX and CB spectral noise levels was also observed. Taking each road surface individually, an excellent spectral correlation was observed, leading to a very accurate estimation of the overall CB noise levels from the CPX noise levels. Considering each one-third octave band frequency, the correlations between CPX and CB spectral noise levels were also good and enable to estimate the overall CB noise levels with the same accuracy as when using the correlation between the overall CPX and CB noise levels. As a perspective, the results could help to compare different tyre/road noise prediction models which have been calibrated or validated with different testing method (pass-by or close-proximity).